Process and an arrangement at suction element

ABSTRACT

The invention relates to a process for collecting process water at a paper machine or the like, wherein water from several suction elements ( 2 . . . 2   n   , 2   m ) provided at a wire ( 1 ) is led in such a way that an unbroken liquid column is maintained in the outlet pipes ( 8 . . . 8   n   , 8   m ) of the suction elements and is made to join a common collecting vessel ( 9, 9   m ). The liquid levels ( 20 . . . 20   n ) of the outlet pipes am regulated by regulating the liquid level ( 11 ) in at least one separate level vessel ( 10 ) towards which the water from the respective outlet pipes is led in at least one closed and essentially horizontal collecting channel ( 9, 9   m ) which is common for several outlet pipes. ( 8 . . . 8   n   , 8   m ), the liquid in said collecting channel ( 9, 9   m ) at the same time forming the lower part of said unbroken liquid column. The invention also relates to an arrangement for collecting process water, wherein the collecting vessel is composed of at least one essentially closed collecting channel ( 9, 9   m ) to which outlet pipes connect below the liquid level.

The present invention relates to a process for collecting process waterat a paper machine or the like, wherein water from several suctionelements provided at the wire is led in such a way that an essentiallyunbroken liquid column is maintained in the respective outlet pipes ofthe respective suction elements and said liquid column is made to joincommon collecting vessels. The invention also relates to an arrangementfor collecting process water at a paper machine or the like, saidarrangement comprising suction elements provided under the wire sectionsaid suction elements being connected by essentially vertical outletpipes to at least one collecting vessel.

In the case of prior known papermachines and the like machines havingsuction elements in the form of suction boxes, the outlet pipes fromsaid elements are generally connected to an essentially open collectingvat, which at the same time often functions as a deaerating means forthe air contained in the water. The process water is generally at leastpartially returned from this collecting vat for joining a suitable phasein the initial part of the process in order to re-use a part of thematerial and the energy remaining in this water and also in order toreduce the amount of effluents from the process.

Since this so called long system should be able to balance the processboth at start-up and during normal operation as well as in case of anyoperational disturbances, the system normally comprises huge amounts ofliquid, which, on the other hand, results in a slow circulation and aprocess with a tendency to contamination, Since this long system extendsover a large portion of the machine, it generally includes many longextensions with inclined or horizontal pipes. Practice has shown thatthese pipes often create problems since the air which always remains inthe water easily forms air pockets which, in turn, results in aninstable process with disturbances in pumps and other equipment. The airalso causes unwanted foaming which is deposited on free surfaces intanks and pipes and creates additional disturbances. In order toalleviate these problems, the system generally includes specialdeaerating means for removing as much air as possible from the water inorder to enable pumping to different parts of the machine. In practiceit is, however, difficult to make these deaerating means sufficientlyeffective without at the same time creating disturbances in the actualliquid flow. Therefore, a significant amount of unwanted air will inpractice always be present in the process water.

Since the long system comprises said huge volumes and long pipe lines,it is in practice also difficult to maintain uniform flow conditions atall points. Stagnant water is thus a common problem and it results inaccumulations of dirt in dead angles of the system. This dirtcontributes to disturbances by occasionally breaking loose and byfollowing the liquid flow in the form of accumulations which then chokeup pumps and valves and which cause quality problems in the actualproduct.

In order to maintain the function in the suction elements it isimportant that the liquid column in the barometric outlet pipes of thesuction boxes is kept unbroken. In the prior art this has been solved byconnecting the pipes to one or more substantially open lock water tanksfrom which the water is pumped to the process. In practice the tankshave to be big since the pumps need a certain inlet pressure in order tofunction satisfactorily. At the same time the huge volumes causeproblems with contamination and they also complicate quick changes inthe production, such as changes in quality and the like. Since the pipelines in practice include long extensions, it is also difficult to avoidthe formation of air pockets which interrupt the vacuum and causeoperational problems. The voluminous systems in themselves also causetroubles since it is not always easy to find suitable places for thespace consuming systems.

The object of the present invention is to provide a solution to theseproblems and to provide an arrangement with a small liquid volume,little contamination risks and a minimal part of free liquid surfaces.At the same time the object is to provide an effective deaeration and areduction in the drawbacks which are caused by an unwanted foaming. Thearrangement should also offer simple and effective means for controllingthe process.

Said objects are provided according to the invention in the waydisclosed in the appended claims. Thus, the process according to theinvention is characterized in that the liquid levels of the outlet pipesare regulated by regulating the liquid level in at least one separatelevel vessel towards which the water from the respective outlet pipes isled in at least one closed and essentially horizontal collecting channelwhich is common for several outlet pipes in such a way that the liquidin said collecting channel at the same time forms the lower part of saidunbroken liquid column. The arrangement according to the invention ischaracterized in that the collecting vessel is composed of at least oneessentially closed and generally horizontal collecting channel to whichsaid outlet pipes connect below the channel liquid level.

A preferred embodiment of the invention is generally described below asan example with reference to the appended drawings, wherein

FIG. 1 discloses a general view of an arrangement according to anembodiment of the invention,

FIG. 2 discloses an alternative embodiment of the connection between theoutlet pipes and the horizontal collecting channel according to theinvention,

FIG. 3 discloses a preferred connection of a barometric pipe from asuction box to the collecting pipe,

FIG. 4 shows a greatly exaggerated section of a collecting channel suchthat the bottom of the channel is arranged to be essentially horizontalwhile its top portion is arranged to be inclined, whereby the height ofthe channel increases in the direction towards the level vessel, and

FIGS. 5a to 5 c disclose different alternative cross sections of thecollecting channel according to the invention.

The arrangement according to FIG. 1 generally comprises a paper machineor the like machine wherein a material web 1 running in the direction ofthe arrow is arranged in a way known per se so that liquid from the webis separately sucked out by suction elements provided in the form ofsuction boxes 2, 2 a . . . 2 n or the like elements. A back water trayor save-all tray 3, 3 a for collecting water which is not sucked out bythe suction boxes 2 is arranged under the wire. The save-all tray isgenerally divided so that a portion 3, which lies early in the processdirection, leads the process water to the so called short system orcirculation 4 while a portion 3 a, which lies later in the processdirection, leads the process water towards the so called long system 5.In the illustrated preferred embodiment the pumping of these processwater portions is performed with degassing pumps 6, 7 which aredescribed in greater detail e.g. in U.S. Pat. No. 5,861,052.

In order to maintain a suitable vacuum and an appropriate dewatering inthe suction boxes 2, 2 a . . . 2 n, which are suitably arrangedsuccessively along the material web 1, the outlet pipes 8 . . . 8 n ofthe suction boxes are provided in the form of so called barometric pipeswhose upper parts are connected to the suction boxes in a way known perse. According to the invention, the lower parts 16 of the respectiveoutlet pipes 8 . . . 8 n are connected to a common collecting channel 9via special elements so that the connection 17 lies under the surface 18of the liquid 19 in the channel 9, as is more clearly shown e.g. in FIG.5a.

In the embodiment shown in FIG. 1 the collecting channel 9 is disclosedas one single channel, but in practice the channel may also be dividedinto several separate channels arranged in parallel and/or successively.Parallel channels 9, 9 m may further be arranged so that each respectivechannel collects only or mainly liquid of a certain consistency or of acertain origin for further treatment in accordance with the specialrequirements of that specific liquid fraction. Parallel channels 9, 9 mmay further be used e.g. in case of successive modifications of priorexisting plants which have another kind of collecting system, as well asfor transporting water e.g. from the suction box 2 m of a top wire,either in combination with water from elsewhere or separately. In FIG. 1such an arrangement is schematically indicated by a partly broken linewith the reference numerals 8 m and 9 m, respectively.

FIG. 1 shows with level indications 20, 20 n how the vacuum in therespective suction boxes 2, 2 a . . . 2 n, 2 is arranged. Thus, thevacuum increases in the process direction as the web 1 becomes drier andreleases less water. Water and air which is sucked into the suctionboxes 2, 2 a . . . 2 n flows down along the barometric pipes and 8 . . .8 n and is led into a common liquid stream 19 in the substantiallyhorizontal collecting channel 9. A certain segregation takes placetherein so that the water flows along the bottom of the channel whileair and foam 21 accumulate at the top 22 of the channel 9. The movementin the horizontal collecting channel 9 is primarily maintained with theaid of the pump 7. According to a preferred embodiment, a part of themovement is caused by the air enclosed in the water owing to the factthat the collecting channel 9 or especially its top portion 22 as suchis arranged to rise slightly in the direction of the pump 9, which isshown with exaggeration in FIG. 4. According to an embodiment which isshown, for instance, in FIG. 5b, the top portion is further designed asa special channel 22 a for the foam.

According to the invention, the collecting channel 9 is connected to alevel vessel 10 having a free surface 11. Said level vessel 10 is used,on one hand, for controlling the actual process by enabling variation ofthe level of the liquid surface 11, which is shown by a broken line inFIG. 1. This general level exists in the shown embodiment also at thefree liquid surface 12 at the opposite end of the collecting channelwhich is suitably connected to the back portion 3a of the save-all tray.On the other hand, the same level vessel 10 is preferably used also as afoam separator, as disclosed in greater detail below.

At start-up of the system according to the invention care is taken toascertain that the water level in the level vessel 10 reaches up to asufficient height. This will automatically ensure that substantially thesame water level is provided during the start-up also in the collectingpipes 8 . . . 8 n, which automatically prevents the collecting pipesfrom being emptied by the suction caused by the vacuum applied to thesuction boxes.

When water and foam flow in the collecting channel 9, at least the foam21 will suitably first encounter an inlet channel 13 to the level vessel10. At this inlet the foam 21 and most of the air rises upwards to thesurface 11 of the level vessel, from where the foam is removed in asuitable way. The direction of movement in the inlet channel 13 isindicated by an upwards directed arrow. The energy for this movement issuitably provided by the air contained in the water. Having reached thesurface 11, the water is suitably led back to the collecting channel 9via an outlet channel 14 which is located closer to the inlet of thepump 7. This results in a continuous liquid movement which is primarilycaused by the difference in specific weight between the foaming liquidand the liquid from which the foam 21 has been removed. In addition tothe water which derives from the collecting channel it is also suitableto direct process water from elsewhere, in the shown case e.g. waterfrom the short system via an overflow 15, to the level vessel 10,suitably to a point above its highest surface 11. In order to preventstagnation in the level vessel an embodiment of the invention comprisesintroducing such water tangentially at the wall of the level vessel 10,whereby a certain rotation is maintained in the vessel 10.

The collecting channel 9 is preferably construed as a continuous, even,suitably slightly rising, and substantially horizontal channel. Thereshould not be any pockets or other points where foam 21 and dirt mayaccumulate. At the same time, the total liquid volume in the collectingpipe 9 is much smaller than in conventional arrangements. This providesa large flexibility for instance for quick quality changes. Thearrangement also results in a radically reduced sensitivity todisturbances in the whole system.

As shown especially in FIGS. 5a to 5 c, the outlet pipes 8 . . . 8 n areconnected to the collecting channel 9 in such a way that the orifices 17of the pipes are all the time below the liquid surface 18 in the channel9. FIG. 1 shows generally an especially preferred embodiment wherein thepipes 8 are connected directly to the side of the channel. In anotherembodiment, which is shown in FIG. 2, the pipes 8 . . . 8 n are attachedto the channel in such a way that they connect to the bottom of thechannel 9 via a bend 16 a. This arrangement actually provides aguarantee against a collapse of the liquid column in the pipe 8 as aresult of a too low liquid level in the collecting channel 9. However,the bends 16 a must be very carefully designed in order to preventaccumulation of contaminants. The embodiments of FIGS. 1 and 3 are inthis respect less sensitive to disturbances since the connection betweenthe pipe 8 and the channel 9 is generally horizontal and preferably evenslightly downwards inclined, whereby an accumulation of dirt iseffectively prevented. In order to further reduce the volume of thesystem, the outlet pipes 8 . . . 8 n, 8 m are suitably construed in sucha way that their diameter below the liquid surface of the level vessel10 is smaller than their volume above said surface, as is shown withrough exaggeration with the reference numeral 8 a in FIG. 1.

FIGS. 5a to 8 c show that the collecting channel 9 is preferablyconstrued so as to promote an accumulation of foam 21 in its upper part.Thus, the channel 9 preferably has a generally oval cross section, whichin certain cases may be provided with separate spaces 22 a for foam 21as is shown in FIG. 5b. In the embodiment according to FIG. 4, the crosssection of the channel is generally rectangular. The height of thechannel cross section increases in the direction towards the pump 7,while the width remains essentially unchanged and the bottom of thechannel is suitably horizontal. This results in a channel whose“ceiling” 22 rises in the direction towards the inlet 13 of the levelvessel 10 enabling especially the foam 21 to follow this rise.

In the text above some preferred embodiments of the invention have beendisclosed as examples, but it is obvious for a person skilled in the artthat the invention can be varied also in many other ways within thescope of the appended claims. Thus, the arrangement may, for instance,be supplemented with suction boxes at a top former arranged above thewire or with other similar devices, from which barometric pipes leaddown to the collecting channel 9 or 9 m in a corresponding way.Moreover, the liquid which is led to the respective channel may betreated either separately alone or in combination with other liquid(s)from some other part of the process.

What is claimed is:
 1. A process for collecting process water at a papermachine or the like, wherein water from several suction elements (2 . .. 2 n, 2 m) provided at a wire (1) is led in such a way that anessentially unbroken liquid column is maintained in the outlet pipe (8 .. . 8 n, 8 m) of each respective suction element (2 . . . 2 n, 2 m) andis made to join a common collecting vessel (9, 9 m), wherein the liquidlevels (20 . . . 20 n) of the outlet pipes (8 . . . 8 n, 8 m) areregulated by regulating the liquid level (11) in at least one separatelevel vessel (10) towards which the water from the respective outletpipes (8 . . . 8 n, 8 m) is led in at least one closed and essentiallyhorizontal collecting channel (9, 9 m) which is common for severaloutlet pipes (8 . . . 8 n, 8 m) in such a way that the liquid in saidcollecting channel (9, 9 m), which as such leads the liquid onwards, atthe same time forms the lower part of said unbroken liquid column.
 2. Aprocess according to claim 1, wherein a part of the process water is ledto said level vessel, suitably so that at least a part (15) of saidprocess water derives from another part of the process (3), andoptionally comprises water from an overflow in connection with the shortsystem of the machine.
 3. A process according to claim 1 or 2, in thatwherein process water collected in a save-all tray (3, 3 a) is led tosaid common collecting channel (9, 9 m), optionally so that the water inthe horizontal collecting channel (9, 9 m) is allowed to move towardsthe level vessel (10).
 4. A process according to claim 1, wherein thepumping out from the system is controlled by regulating the liquid level(11); in the level vessel (10), suitably so that the level during theoperation of the machine is kept at a lower level than at start-up inorder to maintain the balance of the system.
 5. An arrangement at apaper machine for collecting process water, said arrangement comprisingsuction elements (2 . . . 2 n, 2 m) provided at a wire section or thelike, said suction elements being connected by essentially verticaloutlet pipes (8 . . . 8 n, 8 m) to at least one collecting vessel,wherein said collecting vessel is composed of at least one essentiallyclosed collecting channel (9, 9 m) to which said outlet pipes connectbelow the liquid level of the channel.
 6. An arrangement according toclaim 5, wherein the collecting channel (9, 9 m) is connected to a levelvessel (10) having a free liquid surface (11), suitably so that thelevel vessel (10) comprises an inlet (13) from the collecting channel(9, 9 m) and a separate outlet (14) which is provided in the flowdirection behind the inlet (13), optionally so that the inlet (13)and/or the outlet (14) are arranged in the lower part of the levelvessel (10) below the liquid level (11) in the level vessel (10).
 7. Anarrangement according to claim 6, wherein in addition to said outletpipes (8 . . . 8 n, 8 m) from the suction elements (2 . . . 2 n, 2 m), afurther inlet (8 p) from the same and/or another part of the process,suitably from the save-all tray (3, 3 a), is connected to the horizontalcollecting channel (9, 9 m).
 8. An arrangement according to claim 6 or7, wherein a separate inlet (15) for process water from another part ofthe process, suitably from an overflow in connection with the shortsystem of the machine, is connected to the level vessel (10).
 9. Anarrangement according to claim 6, wherein the collecting channel (9, 9m) at least in certain parts is constructed with a cross section havinga height which is substantially larger than its width.
 10. Anarrangement according to claim 6, wherein the collecting channel (9, 9m) comprises a special portion (21) for accumulation of air and/or foampresent in the liquid.
 11. An arrangement according to claim 6, whereinthe collecting channel is arranged substantially horizontally, suitablyso that at least a part of the channel (9, 9 m) is slightly ascending inthe direction towards the level vessel (10).
 12. An arrangementaccording to claim 6, wherein the collecting channel consists of severalseparate channel sections (9, 9 m) and/or includes branchings or thelike.
 13. A process according to claim 2, wherein the pumping out fromthe system is controlled by regulating the liquid level (11); in thelevel vessel (10), suitably so that the level during the operation ofthe machine is kept at a lower level than at start-up in order tomaintain the balance of the system.
 14. An arrangement according toclaim 8, wherein the collecting channel (9, 9 m) at least in certainparts is constructed with a cross section having a height which issubstantially larger than its width.
 15. An arrangement according toclaim 14, wherein the collecting channel is arranged substantiallyhorizontally, suitably so that at least a part of the channel (9, 9 m)is slightly ascending in the direction towards the level vessel (10).